The objective of this research is to study the changes in rat tracheal mucin synthesis and secretion upon chronic exposure to SO2 (or H2SO4), an inducer of experimental chronic bronchitis. The changes will be followed both histochemically and biochemically in order to establish a structure-function relationship. Initially, two systems will be explored and fully developed in which to expose the rat trachea to SO2 (or H2SO4). These are tracheal transplants and organ cultures of tracheal explants. Each will be exposed to SO2 (or H2SO4) followed by histochemical examination of the tissue. The secretions will be characterized biochemically, after purification by column chromatography and agarose-acrylamide electrophoresis. Alterations in the mucus will be based on: total amount of mucin; molecular weight of the mucin fraction and mucin subunits; and relative charge, and sugar, sulfate, and amino acid analysis of the mucin subunits. These procedures will be used to obtain a molecular marker(s), characteristic of the condition, with which to study the progression and regression of the disease.